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  Java Practices -> Internationalization
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<div class='page-title'>Internationalization</div>

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<br>Some applications need to use more than one language in the user interface. 
Changing a program to allow for this is called "internationalization", while the 
actual translation is called "localization". Translation is usually applied only to user 
interface elements (menus, labels, and so on), and <em>not</em> to business data stored in the database.

<P>Most implementations of multilingual applications use 
<tt><a href="http://java.sun.com/javase/6/docs/api/java/util/ResourceBundle.html">ResourceBundle</a></tt> and 
<tt><a href="http://java.sun.com/javase/6/docs/api/java/util/Locale.html">Locale</a></tt>. However, there 
are some problems with this style, so one might <a href="TopicAction7ee5-2.html">consider alternatives to ResourceBundle</a>.

<P>Here is a simple illustration of the basic <tt>ResourceBundle</tt> mechanism :

<p><tt>BankMachine</tt> is a user of a <tt><a href="http://java.sun.com/javase/6/docs/api/java/util/ResourceBundle.html">ResourceBundle</a></tt>,
whose <tt><a href="http://java.sun.com/javase/6/docs/api/java/util/Locale.html">Locale</a></tt>
is set by the end user. This illustration uses 
<tt><a href="http://java.sun.com/javase/6/docs/api/java/util/ListResourceBundle.html">ListResourceBundle</a></tt>, 
but 
<tt><a href="http://java.sun.com/javase/6/docs/api/java/util/PropertyResourceBundle.html">PropertyResourceBundle</a></tt> 
is likely used more often.

<br>
<PRE>

<span class='keyword'>import</span> java.util.ResourceBundle;
<span class='keyword'>import</span> java.util.Locale;

<span class='keyword'>public</span> <span class='keyword'>final</span> <span class='keyword'>class</span> BankMachine {

  <span class='comment'>/**
  * Run first a French version, then an English version.
  */</span>
  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>void</span> main(String[] aArguments) {
    BankMachine bankMachine = <span class='keyword'>new</span> BankMachine();
    bankMachine.selectLanguage( fFRENCH );
    bankMachine.showDisplay();
    bankMachine.selectLanguage( fENGLISH );
    bankMachine.showDisplay();
  }

  <span class='comment'>/**
  * The user's first action is to select a language.
  */</span>
  <span class='keyword'>public</span> <span class='keyword'>void</span> selectLanguage( String aLanguage ) {
    <span class='keyword'>if</span> ( aLanguage.equals(fENGLISH) ) {
      fText = ResourceBundle.getBundle(fBUNDLE_NAME, Locale.ENGLISH);
    }
    <span class='keyword'>else</span> <span class='keyword'>if</span> ( aLanguage.equals(fFRENCH) ) {
      fText = ResourceBundle.getBundle(fBUNDLE_NAME, Locale.FRENCH);
    }
    <span class='keyword'>else</span> {
      <span class='keyword'>throw</span> <span class='keyword'>new</span> IllegalStateException(<span class='literal'>"Unknown language"</span>);
    }
  }

  <span class='keyword'>public</span> <span class='keyword'>void</span> showDisplay() {
    <span class='comment'>//use the bundle to get the proper version of a string
</span>    <span class='comment'>//note that the variable names - Text.Hello, etc -  reflect the content,
</span>    <span class='comment'>//so these method calls clearly indicate what is being displayed
</span>    <span class='comment'>//to the user
</span>    System.out.println(fText.getString(Text.Hello));
    System.out.println(fText.getString(Text.PleaseSelectAction));
  }

  <span class='comment'>/// PRIVATE ///
</span>  <span class='keyword'>private</span> <span class='keyword'>static</span> String fENGLISH = Text.English;
  <span class='keyword'>private</span> <span class='keyword'>static</span> String fFRENCH = Text.French;
  <span class='keyword'>private</span> <span class='keyword'>static</span> String fBUNDLE_NAME = <span class='literal'>"Text"</span>;

  <span class='comment'>/**
  * Default is English.
  * Note that this default is perfectly suitable for any initial user
  * selection of language, since the Strings representing the languages
  * themselves have only one representation, which are defined in the
  * default bundle.
  */</span>
  <span class='keyword'>private</span> ResourceBundle fText = ResourceBundle.getBundle(fBUNDLE_NAME, Locale.ENGLISH);
}
 
</PRE>
<br>
<br>An example run of <tt>BankMachine</tt> gives:
<p><tt>Bonjour</tt>
<br><tt>Veuillez choisir une action</tt>
<br><tt>Hello</tt>
<br><tt>Please select an action</tt>
<p>The default <tt>ResourceBundle</tt> contains both constants and the
default representations of all text :
<br>
<PRE>

<span class='keyword'>import</span> java.util.*;

<span class='keyword'>public</span> <span class='keyword'>class</span> Text <span class='keyword'>extends</span> ListResourceBundle {

  <span class='keyword'>public</span> <span class='keyword'>final</span> Object[][] getContents() {
    <span class='keyword'>return</span> fContents;
  }

  <span class='comment'>/**
  * These constants are used by the caller to identify what text is
  * needed; which version of the text is actually returned is determined
  * by the ResourceBundle mechanism.
  *
  * Using variable names which reflect the content clarifies the
  * intent of the code in the user of this class.
  */</span>
  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>final</span> String Hello = <span class='literal'>"Hello"</span>;
  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>final</span> String PleaseSelectAction = <span class='literal'>"PleaseSelectAction"</span>;

  <span class='comment'>/**
  * Language names presented as a list of choices to the user
  * are special, since they are always presented in the native language.
  * Thus, this default bundle defines the
  * unique representations of all language names, and no other
  * bundle provides a translation for them.
  */</span>
  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>final</span> String English = <span class='literal'>"English"</span>;
  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>final</span> String French = <span class='literal'>"Francais"</span>;

  <span class='comment'>/// PRIVATE ///
</span>  <span class='keyword'>private</span> <span class='keyword'>static</span> <span class='keyword'>final</span> Object[][] fContents = {
    { Text.Hello, <span class='literal'>"Hello"</span> },
    { Text.PleaseSelectAction, <span class='literal'>"Please select an action"</span> } ,
    { Text.English, <span class='literal'>"English"</span> },  <span class='comment'>//never defined elsewhere
</span>    { Text.French, <span class='literal'>"Francais"</span> },  <span class='comment'>//never defined elsewhere
</span>  };
}
 
</PRE>
<br>
<p>The other <tt>ResourceBundle</tt> classes do not define constants, just
the translations :
<br>
<PRE>

<span class='keyword'>import</span> java.util.*;

<span class='keyword'>public</span> <span class='keyword'>class</span> Text_fr <span class='keyword'>extends</span> ListResourceBundle {

  <span class='keyword'>public</span> <span class='keyword'>final</span> Object[][] getContents() {
    <span class='keyword'>return</span> fContents;
  }

  <span class='comment'>//No constants are defined here
</span>
  <span class='comment'>/// PRIVATE ///
</span>  <span class='keyword'>private</span> <span class='keyword'>static</span> <span class='keyword'>final</span> Object[][] fContents = {
    { Text.Hello, <span class='literal'>"Bonjour"</span> },
    { Text.PleaseSelectAction, <span class='literal'>"Veuillez choisir une action"</span> }
  };
}
 
</PRE>
<br>
<br>
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<div class='topic-section'>See Also :</div>
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  <a href='TopicAction7ee5-2.html?Id=208'>Try alternatives to ResourceBundle</a> <br>
 
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